1. Field of the Invention
The present disclosure relates to zirconium alloys for a nuclear fuel cladding having a superior oxidation resistance in a severe reactor operation condition and methods of preparing a zirconium alloy nuclear fuel cladding by using thereof; and more particularly, to zirconium alloys for a nuclear fuel cladding having a superior oxidation resistance and applicable for a power uprate, a load follow, an ultra high burnup and an ultra long cycle operation, and methods of preparing a zirconium alloy nuclear fuel cladding by using thereof.
2. Description of the Related Art
As nuclear fuel used in a nuclear power plant for power production in operation, a zirconium alloy for a nuclear fuel cladding is used. Nowadays, a zirconium alloy such as Zircaloy-4, Zircaloy-2, ZIRLO, M5, etc. is used as the nuclear fuel cladding. However, Zircaloy-4 commonly used as the nuclear fuel cladding in a power plant from 1960s are recently replaced with a novel alloy such as ZIRLO, M5, etc. The novel alloy including ZIRLO and M5 has a good corrosion resistance in a normally operating reactor when comparing with the commonly used Zircaloy-4 and contributes to the improvement of the performance of the nuclear fuel. Through the improvement of the corrosion resistance of the nuclear fuel cladding, the nuclear fuel may be used safely for an extended time period, thereby improving the economic efficiency of a nuclear power generation.
The improvement of the corrosion resistance, which is the most important characteristic of the nuclear fuel cladding under development, may be accomplished by appropriately combining alloying elements along with a manufacturing method. Particularly, the corrosion resistance of the nuclear fuel cladding may be remarkably increased by using niobium (Nb) as a main element among the alloy elements of the zirconium alloy, when comparing with Zircaloy-4 alloy. However, the zirconium alloy including the niobium may have quite different phase transition properties from Zircaloy-4 alloy. Thus, the development on a manufacturing technology according to the change of the alloy elements is also necessary at the same time.
Technology on improving the corrosion resistance of the zirconium alloy through the adjustment of the alloy elements and the control of a heat treatment are disclosed as follows.
U.S. Pat. No. 6,125,161A discloses a method of preparing a zirconium alloy nuclear fuel cladding including 0.2 to 1.7 wt % of tin, 0.18 to 0.6 wt % of iron, 0.07 to 0.4 wt % of chromium and 0.05 to 1.0 wt % of niobium.
JP 8067954A discloses a method of preparing a zirconium alloy nuclear fuel cladding including 0.4 to 1.7 wt % of tin, 0.25 to 0.75 wt % of iron, 0.05 to 0.3 wt % of chromium, 0 to 0.1 wt % of nickel and 0 to 1.0 wt % of niobium.
U.S. Pat. No. 4,649,023A discloses a method of preparing a zirconium alloy including 0.5 to 2.0 wt % of niobium, 0 to 1.5 wt % of tin, and 0.25 wt % of at least one element selected from the group consisting of iron, chromium, molybdenum, vanadium, copper, nickel, and tungsten.
U.S. Pat. No. 5,844,959A discloses a zirconium alloy for a nuclear fuel cladding including 0.5 to 3.25 wt % of niobium and 0.3 to 1.8 wt % of tin.
Operating conditions of a reactor have been continuously changed to a direction of increasing the economic efficiency of a nuclear power generation. As the operating conditions for increasing the economic efficiency of the nuclear power generation, a power uprate, a load follow, an ultra high burnup, an ultra long cycle operation, etc. have been known. Under such operating conditions, even the recently used novel alloy claddings in place of Zircaloy-4 may be expected to hardly maintain integrity for a long time. Accordingly, the development on the cladding maintaining a good performance under severe operating conditions may be an essential factor of the improvement of the economic efficiency in a nuclear power generation.
In addition, among the necessary performance of the cladding, safety under an emergency condition in the event of an accident becomes important more and more.
When a cooling function of a nuclear reactor is malfunctioning in an accident due to a natural disaster such as an earthquake, tsunami, etc. or by a man made hazard, the cladding may be exposed to a high temperature and may be rapidly oxidized, thereby generating hydrogen having a risk of an explosion. The hydrogen explosion generated in a power plant is required to be prevented without fail because the explosion may induce a disaster accompanying the leakage of radioactive substances. Thus, the nuclear fuel cladding is required to have a good oxidation resistance at a high temperature even when exposed to an accident condition. When the nuclear fuel cladding has a good oxidation resistance at a high temperature even in an accident, time for managing may be increased before the hydrogen explosion, and the safety of the nuclear power generation may be remarkably improved. However, the development on the nuclear fuel cladding until now has been conducted for mainly improving the economic efficiency under a normal operation without considering the safety in an accident condition greatly. Thus, the preparation on confirming the safety in an accident condition is urgently in need.
Accordingly, the present inventors have studied on a zirconium alloy nuclear fuel cladding by which the economic efficiency of the nuclear power generation may be increased and the safety in an accident condition also may be improved, and have developed a zirconium alloy having a good oxidation resistance under a normal operating condition of a reactor as well as under accident condition and applicable for a power uprate, a load follow, an ultra high burnup and an ultra long cycle operation.